Air source vs Ground source heat pumps

Air source vs ground source heat pumps: Overview

If you are looking to replace your heating system, a heat pump is one of the most efficient options available. Unlike traditional gas or oil boilers that burn fuel to create heat, heat pumps move existing heat from the outside environment into your home. Because they transfer heat rather than generating it from scratch, they use far less energy than they produce.

When you decide to install a heat pump, your main choice is between an air source system and a ground source system. Both use the same basic technology, but they collect their heat from different places. This single difference changes how much the system costs, how difficult it is to install, and how much space you need outside your property.

Choosing the right option depends on your budget, the size of your garden, and what kind of heating fuel you currently use. This guide explains how both systems work, breaks down the typical costs and government grants available, and helps you decide which type makes the most sense for your home.

How air source heat pumps work

An air source heat pump looks similar to a large air conditioning unit. It sits outside your property, usually mounted on a wall or placed on the ground next to your house. Its job is to take heat from the outside air and boost it to a temperature high enough to warm your home and your hot water.

The unit contains a fan that draws outside air over a network of tubes filled with a special refrigerant fluid. This fluid is extremely sensitive to temperature, meaning it turns into a gas even when the outside air is cold. A compressor then squeezes this gas, which forces its temperature to rise significantly. This concentrated heat is passed into your home's heating system to warm your radiators or underfloor heating, before the refrigerant cools down and the cycle starts again.

The most common type in the UK is an air-to-water heat pump, which links up to your standard wet central heating system (radiators and a hot water cylinder). However, you can also get air-to-air heat pumps. These blow warm air directly into your rooms through wall-mounted units, much like an air conditioning system running in reverse. Air-to-air systems cannot heat your hot water taps, so you would need a separate solution for baths and showers.

Because they draw heat from the air, air source heat pumps are slightly less efficient in the middle of winter when the air is freezing. However, modern units are designed to work perfectly well even in sub-zero temperatures, drawing enough ambient heat from the air to keep a well-insulated house warm.

How ground source heat pumps work

A ground source heat pump uses the same compression cycle as an air source model, but it gathers its heat from the earth instead of the air. Just a metre or two below the surface, the ground temperature in the UK stays relatively constant all year round, usually hovering between 10°C and 12°C. This gives the heat pump a stable, reliable source of warmth, even during the coldest winter months.

To collect this heat, installers must bury a long loop of plastic pipework in your garden. A mixture of water and antifreeze is pumped through this loop. As the fluid travels through the underground pipes, it absorbs the natural heat from the earth. It then returns to the heat pump unit inside your home, where a compressor boosts the temperature to heat your radiators and water cylinder.

There are two ways to install the underground pipework. The first is a horizontal ground loop, where the pipes are laid in shallow trenches about a metre deep. This is the cheapest method, but it requires a very large amount of clear outdoor space — often two or three times the total floor area of your house.

If you do not have enough space for horizontal trenches, the alternative is a vertical borehole. Installers use heavy drilling machinery to bore a hole straight down into the earth, often reaching depths of 50 to 100 metres. The pipe is then fed down the hole. While this takes up very little surface space in your garden, the specialist drilling makes it a much more expensive process.

Comparing the key differences

While both systems achieve the same end result, the practical realities of fitting and running them are very different. Air source systems are the default choice for most standard residential streets, while ground source systems are usually reserved for large rural properties, self-build projects, or major renovations.

The table above highlights the main trade-offs. You pay a heavy premium for a ground source system, both in money and in the disruption to your garden. In return, you get a system that is entirely hidden from view and runs slightly more efficiently, which lowers your monthly heating bills.

Upfront costs and government grants

Heat pump installations are priced on a case-by-case basis. The final bill depends heavily on the size of your property, how much heat you need, and how complex the pipework is. However, average market figures give a clear picture of the price gap between the two technologies.

To help households manage these high upfront costs, the government offers financial support through the Boiler Upgrade Scheme (BUS). Administered by Ofgem, this scheme currently provides a flat £7,500 grant towards the cost of an air source or ground source heat pump in England and Wales. You do not need to claim this money yourself; an MCS-certified installer will apply for the grant and deduct the £7,500 directly from your invoice.

With the standard £7,500 grant applied, the out-of-pocket cost for a typical air source heat pump falls to roughly £500 to £8,500. Ground source installation costs vary substantially, particularly where boreholes or enabling works are needed, so ask for an itemised quote rather than relying on a typical net range. The scheme has been extended to 2029/30, backed by approximately £2.7 billion in funding under the government's Warm Homes Plan.^[1]

Recent rule changes have made the grant easier to access. As of 28 April 2026, you no longer need a valid Energy Performance Certificate (EPC) with no outstanding insulation recommendations to apply. On the same date, the scheme was expanded to offer a £2,500 grant for air-to-air heat pumps. However, the April 2026 rules also strictly excluded hybrid systems (where a heat pump is paired with a traditional fossil fuel boiler) from receiving the £7,500 grant.^[2]

Hidden costs: Radiators, underfloor heating, and electricals

The headline price of the heat pump unit is only part of the story. Because heat pumps operate differently to gas boilers, you often have to upgrade other parts of your home to make the system work properly. If you do not budget for these extra works, the final quote can come as a shock.

Heat pumps run at a lower "flow temperature" than traditional boilers. A gas boiler typically sends water to your radiators at around 65°C to 75°C. A heat pump usually sends water at around 35°C to 45°C. Because the water is cooler, the heat emitter needs a larger surface area to warm the room to the same comfortable temperature. This means you will likely need to replace some or all of your existing radiators with larger, double-panel models. Upgrading a home with new, larger radiators can add around £3,000 to the project.

To maximise the efficiency of a heat pump — especially a ground source system — underfloor heating is the best option. It covers a vast surface area, allowing the heat pump to run at its absolute lowest and most efficient temperature. However, retrofitting underfloor heating into an existing home is highly disruptive and can add approximately £10,000 to the total cost.

You also need to consider your home's electrical setup. Heat pumps draw a large amount of current, especially when they first start up. Many older homes do not have a modern consumer unit (fuse box) capable of handling this extra load. Upgrading your domestic electrical system to safely support the heat pump can add roughly £500 to £2,000+ to your final bill.

Installation process and disruption

The installation process is where the two systems differ most. Fitting an air source heat pump is a relatively straightforward plumbing and electrical job. Assuming you have a suitable spot outside and a place for the hot water cylinder inside, a team can usually complete the work in one to three days. The disruption is similar to having a new boiler fitted, with minimal impact on your garden.

Installing a ground source heat pump is a major construction project. A standard installation takes around 6 working days, and the level of disruption to your property is significant. If you choose a horizontal loop system, a team with a mechanical digger will need to excavate large, shallow trenches across your lawn. If you choose a vertical system, a specialist drill rig must be driven onto your property to bore deep into the ground.

Once the ground source system is in place, all the outdoor pipework is completely hidden. However, homeowners must factor in the cost, time, and effort of re-turfing or landscaping the garden afterwards, which is rarely included in the installer's quote.

Efficiency and winter performance

Both types of heat pump are incredibly efficient compared to traditional heating. A brand-new gas boiler operates at about 90% to 94% efficiency, meaning it turns roughly 90% of the gas it burns into useful heat, while the rest is lost as waste gases out of the flue.

Heat pumps operate above 100% efficiency because they move heat rather than creating it. An air source heat pump typically operates at around 250% to 350% efficiency. This means that for every 1 unit of electrical energy it uses to run the compressor, it delivers roughly 2.5 to 3.5 units of heat into your home. A 2026 analysis by HeatPumpMonitor.org showed that well-designed air source heat pumps achieve a high average Seasonal Performance Factor (SPF) of around 3.86 over the course of a year.

Ground source heat pumps boast even higher efficiencies, typically sitting at approximately 300% to 400%+. Because the ground stays at a steady 10°C to 12°C all winter, the pump does not have to work as hard to extract heat. An air source pump, by contrast, has to work slightly harder when the outside air drops below freezing.

Despite this, the idea that air source heat pumps fail in cold weather is a myth. Real-world data contradicts it heavily. A 2026 survey by Octopus Energy, conducted during a severe cold snap, found that approximately 85% of heat pump owners were satisfied with their system's cold-weather performance. In contrast, only around 80% of gas boiler users reported being satisfied during the same period.

Running costs and bill savings

Because a ground source heat pump is more efficient, it will use less electricity than an air source model to generate the exact same amount of heat. Over the course of a year, this gives ground source systems the edge on running costs.

However, whether a heat pump saves you money overall depends on what heating fuel you are moving away from. Electricity is significantly more expensive per unit than natural gas. Even though a heat pump uses three to four times less energy than a gas boiler, the higher price of electricity means your running costs might stay roughly the same if you switch from mains gas. You will need a highly efficient system and a dedicated heat pump energy tariff to see noticeable savings on your monthly bills.

Off-grid homes may have greater scope to save, especially when replacing LPG or electric storage heating, but savings are not guaranteed: they depend on system design, heat demand and the electricity tariff. The temporary £9,000 grant uplift is specifically for eligible off-gas-grid homes replacing oil or LPG.^[1]

Planning permission and noise rules

In England, an air source heat pump will often be permitted development, so formal planning permission is not normally needed. Since May 2025, the previous one-metre boundary rule no longer applies in England, but size, siting and noise requirements still apply. Planning rules differ in Scotland, Wales and Northern Ireland, and listed buildings or protected areas may need additional consent, so check with your local planning authority.

Noise is a practical factor to consider with air source systems. The fan and compressor make a continuous humming sound when running, similar to a modern fridge or an air conditioning unit. While they are not overly loud, you should place the unit away from bedroom windows and consider how the noise might affect your neighbours.

Ground source heat pumps are generally easier to get past planning regulations because the heat-collecting pipework is entirely hidden underground. The indoor unit, which is roughly the size of a large fridge-freezer, does make a low-level hum, but it is contained inside your utility room or garage. From January 2026, Ofgem also began regulating heat networks, meaning if you share a ground loop system with neighbours, the operator must comply with strict consumer protection and performance standards.

Which homes suit which system?

Not every home is suited to both technologies. Industry experts note that homes often labelled as "never suitable" for a heat pump are usually just highly inefficient properties that need better insulation, rather than a failure of the heat pump technology itself. To get the best out of either system, your home needs to be well-insulated with good double glazing and loft insulation.

The government is also pushing the wider heating industry to adapt. Under the Clean Heat Market Mechanism (CHMM), qualifying boiler manufacturers must obtain heat-pump credits linked to their relevant fossil-fuel boiler sales. This is a manufacturer obligation, not a requirement for householders.